c# - 在 AspNetCore 中构建/实例化静态类的正确方法

Question

我在 ASPNetCore 2017 中构建了这个静态 AppSettings 类的工作示例。我想知道是否有更简单/更好的方法来做到这一点。我是新手，所以我希望得到一些专家建议..

我正在使用 MiddleWare 组件来实例化包含所有 Json appSettings 值的静态 AppSettings 类。我这样做是因为我不希望 Controller 类必须知道如何设置它要查询的数据库的连接字符串。我正在使用 SQLClient(不是 EF，因为我所有的调用都是对存储过程的调用)。

这是我的代码:

appSettings.Json

{ “应用程序设置”:{ "WarehouseConnectionString": "Data Source=[Removed]\SQLExpress;Initial Catalog=Warehouse;Integrated Security=True;" },

AppSettings 类

public class AppSettings
{       
    public AppSettings()
    {
        // Set default values of our options.
        WarehouseConnectionString = "WarehouseConnectionString";
    }

    /// <summary>
    ///  Our Warehouse DB Connection string.
    /// </summary>
    public static string WarehouseConnectionString { get; set; }
}

我的中间件类:

public class ApplicationSettingsService
{
    private readonly RequestDelegate next;

    public ApplicationSettingsService(RequestDelegate next)
    {
        this.next = next;
    }

    public async Task Invoke(HttpContext context, IOptions<AppSettings> appSettings)
    {            
            // Create our static instance of our AppSettings class.                
            AppSettings _settings = appSettings.Value;

            await next(context);            
    }
}

我的 Starup.cs 类

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables();
        Configuration = builder.Build();
    }

    public IConfigurationRoot Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        //************************************************//
        // Adds services required for using options.
        //************************************************//
        services.AddOptions();

        //**********************************************************************//
        // Register the IConfiguration instance which MyOptions binds against the 
        // AppSettings section of the appsetting.json file only.
        //**********************************************************************//
        services.Configure<AppSettings>(Configuration.GetSection("AppSettings"));         

        // Add framework services.
        services.AddMvc();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(Configuration.GetSection("Logging"));
        loggerFactory.AddDebug();

        //******************************************************//
        // Add our own custom Application Settings Middleware     //
        //******************************************************//             
        app.UseMiddleware<ApplicationSettingsService>();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
            app.UseBrowserLink();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
        }

        app.UseStaticFiles();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                //template: "{controller=Home}/{action=Index}/{id?}");
                template: "{controller=Box}/{action=Index}/{id?}");
        });
    }
}

使用 AppSetting 值的我的数据库连接类。

public static class DBConnection
{
    private static string ConnectionString = AppSettings.WarehouseConnectionString;


    public static SqlConnection GetConnection()
    {
        return new SqlConnection(ConnectionString);
    }
}

当客户端( Controller )调用数据库类时，他们不必指定连接字符串，“仓库”已经知道它应该连接到哪个数据库...

   DHRIM5_StoredProcedureDatabaseExample.Data.Warehouse.StoredProcedures sp = new Data.Warehouse.StoredProcedures();

    // GET: Box
    public ActionResult Index()
    {            
        IList<Box> tests = sp.SPGetBoxes().ToList();            
        return View(tests);
    }

感谢您的帮助。

Answer 1

一般来说，您应该避免依赖于基础架构的静态类，因为很难对此类类进行单元测试。但是您可以在单例范围内使用非静态类，因此您将只有一个实例。在你的情况下 - AppSettings.cs

public class AppSettings
{
    public AppSettings()
    {
        // Set default values of our options.
        WarehouseConnectionString = "default_value_if_needed";
    }

    public string WarehouseConnectionString { get; set; }
}

在Startup.cs从 Configuration 获取值(value)并将其注册为单例。

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddMvc();

    var appSettings = Configuration.GetSection("AppSettings").Get<AppSettings>();
    services.AddSingleton(appSettings);
}

然后你可以把这个值注入(inject)到构造函数中

public class DBConnection
{
    private readonly string connectionString;

    public DBConnection(AppSettings settings)
    {
        this.connectionString = settings.WarehouseConnectionString;
    }

    public SqlConnection GetConnection()
    {
        return new SqlConnection(this.connectionString);
    }
}

注意这种情况AppSettings在启动应用程序中是只读的，所以如果你改变 appsettings.json文件，如果不重新启动应用程序，设置将不会应用。
现在你还应该注册DbConnection作为 Startup.cs 中的单例- services.AddSingleton<DBConnection>();并通过构造函数参数请求其对象。

public class StoredProcedures
{
    private readonly DBConnection connection;
    public StoredProcedures(DBConnection connection)
    {
        this.connection = connection;
    }
}

当然，最好将接口(interface)与实现分开，只使用接口(interface)。